Scan conversion system utilizing resolved writing deflections



2 Sheets-Sheet l F. D. COVELY, 3RD.. El' AL SCAN CONVERSION SYSTEM UTILIZING RESOLVED WRITING DEFLECTIONS April 24, 1956 Filed Jan. 31. 1952 April 24, 1956 F. D. covELY, 3RD., ErAL 2,743,378

SCAN CONVERSION SYSTEM UTILIZING RESOLVED WRITING DEF'LECTIONS 2 Sheets-Sheet 2 Filed Jan. 5l, 1952 0 Hillllll I- www. vii mmm/m |.IIIIY MY/ u rsa M.. a ma, #Mw p m mw. Mm uw .ww IIIQ lu/,l IIIIIII Il Il wm fs mm ,o 5 C 0 a m m F m f 6 n /V 1|||+|| IIII II wm wm nu. N MW n M@ is am f wm @r ws United States .Patent O.

SCAN CONVERSION SYSTEM rU'I'IlIZlllG .RESOLVED WMTIN G .DEFLEC'IIONS iFrank'Coveiyrd Camden, and Louis M. Sceberger,

.This .invention .relates generaliy Sto systems employing electrical storage ktube devices and r' ore particularly to scan 'conversion systems in ywhich 'stored :eiectrical data, lincluding half-tones, .is cyclically' and progressivelyferased and replaced with new data. The .present invention 'is .an 'improvement upon the systemdisclosed .in a coprend- 'mgiapplication led by -FrarilkzD/Covely l3rd fonfDecsem- 153erl i9, 1.951, Serial No. 262,3.77 and entitled. fSc'anf Conversion System with .Progressive fCyclical Erasure -now S. .Patent No. 2,7211 8,1609 :granted :September 20, #1.955

.Presently known scan conversion'ssystems shave been iutilizedfentensively in :a number ofidifferent .radio .navifgation systems. A@ne type of storage device =which;may beus'ed for scanfconversion .is described .in a .copending application, noW abandoned, 'Serial No. 29,746,tled May ,28,1948'by l. Pensaievandf entitled Electrical l:Storage Tube and in a continuation:thereoftSerialNo. 374,478, rtiled August :1-7, .1953. Irlhis rtubefineludes dilierenbe'lec- '.troirtgnrrs disposed on opposite sides ofalstorage target. One of the electron guns, .generally referred Ato :the

Writing gun, zprovides anfelect'rorr beam Whichimay'be =deeoted `to scan lthe storage target iat a .predetermined scanning ratelto establishacharge pattern thereon. -lh'e second electron'. gun, Vcalied ithe reading glm, ,produces electron beam Whichfmaybefdeected lacrosszthe storage Y.target fat .ra diiferent scanning rate to. produce koutput vsignals proportional to the stored signals.

` Tir-systems including a storage `tube ot'sthetype described above, it may be desirable Ito tobtain :m'anyrcopies orfreadings of fthe Ycharge pattern :established non'V the storage target. .These copies .generally :are'obtained by repetitively `scanning the;storage;vtarget Withthe reading 'bean-1. .This repetitve'scanning processfhowever,fgraduallyerases v:the.storedcharge totheex-tent Vthat fhalfitone .signals "-lyingvbetween the maximum and minimum intensity Isig- Inalsfappliedto the :tubeE may notrbezdistinguishableethere- Ifronr. Also, the :'dile'rent ratesof signal y decay fdm'in'g scanning for the different intensity signals lare trouble- Vsomesin:resolving half-tones.

.The fhalf-tone signal response may'be especially :imzportant, for example, in :systems .employing .pictorial -dis- .play 'radarequipment (Teleran). In the reception :of :radar signals reflected. and/ or Vretransrn'itted.from an air- '.craft located behind a'. cloud, it is .apparent Athat :ltherabsence of'lialf-tone resolutionvrnaycause the lre'ectedisig- .nal from Vthe lcloud to mask the signal .from the aircraft. Generally,lbefore asuitable `number ofcopies of such'acharge pattern are made, the stronger signal from 'theaircraft tends tofmergeintotbe weaker, andgenerally -larger .in area, signal from. the cloud. At times when weather Vis particularly bad, Ait sf'obvioustthatfthe floss r of tthisl'ralf-tone.information may complicatetratic control -and/for--other lfunctions.

-Astorage tube especially suited for scan .conversion in such rradi'o navigation.v systems and lhaving improved :half- Ltonesignal .responseis`zdescribed in fa -copending application. Serial No. 259,344, also tiled by L. Pensak on 2,743,378 Patented Apr. 24, 1956 December l, 1951, and yentitled Storage Tube. The operation'of this tube lis such that the reading process does not erasethe signals stored, hence itis ynecessary to provide some'meansindependent of the reading process 'for elec'tingdesirederasure In this tube, erasure may "be accomplished, when "desired, by gating arsuppressor grid on the writing gunside of the storage target to ap'- proximately zero volts and substantially simultaneously :turning on vthe writing beam-electron ygun. The writing beam may then rbe continuously, or in any other` desired ymanner, scanned across the storage target 'toerase the `charge pattern previously established.

While this erasing technique, perse, may be satis- `factory for erasingstored transients-andlllike charge rpatterns, the erasure requirements for *radar scanf conversion generally are more exacting. Thisis ftrue, by way= offex- '-arrip-le, when it is desirable to translate electrical data stored in polar coordinates into la. corresponding `television presentation. While the aforementioned Scan Conversion System 'with Progressive Cyclical Erasure, 'Serial No. .262,377 (now Patent No. 2,718,'6()'9),.is-eifec 'tive :bothin maintaining anup-'to-date store ofinformaation. and .in scan converting ha1f-:tone data, a more :ilexizble system `having fa `wider .eld :of .application is desired. The present invention is suitable not only for scan conversion of .complete 360 'P. P. .I. radar scans, butis especially adapted .for :use withradar systems in which sector .scanning is employed.

.An vobject of the .present invention is to .provide.an:im proved system for the scan conyersioncf .electrical 'data Another vobject of the invention is to provide :a scan conversion .system of the type described having a wider .field of application than presentsystems.

Another lobject of the inventionis to provide amore ilexible scan conversion'system inxwhich the :process of reading-does not erase stored signals.

A further object'of the .invention is to .provide a system for-the scan conversion of lhalf-tone Vinforn'lation which system Vis adapted vfor .resolved .radar deflections.

A still afurther .object-of the invention is to provide a sca-n con-versionsystem for -use with a :radar system yin which sectorscanning lmay be employed.

`Another-'object of the vinvention vis toprovide ya radar scanteonversion iti-which .information stored-fon astorage tube is =cyclically-erased during the tube fdeilection fly-back intervals. v

)In fa' .typical embodiment of ythe invention, .resolved fradardeection signals are -.applied to' a stationary-de filection yoke for -ldeii'ecting 1the writing `of :the half-tone storage tube Areferencedabove. -Radar echo.signals, in "modulating .the Vdelierctions and :intensity .of zthe ywriting vbeam establish. a P. fP. yI. :(plan fpo-sitiondndicator) type .chargepattern on thestorage target. Theterm fP. P.I.?? generally-refers -toy a 360 .-radar .searchl but .here maybe applied'toeither a 360 scansion or tothe search'of any sector thereof. .Aftervradar signalsfrom a givenarea -of.^radar search have 'been stored,.it its-.apparent that further writing without erasure is :undesirable (assumingthat integration is not tozbe obtained) since some-ofthe data previously written may correspond to an object or objects no longer within the 'service area-of the radar system. lt is also undesirable .to kcompletely-erase the .stored .scan since, in a number of radar. systems,: atcertain :amount of time is required .for obtaining acomplete newfscan. Also, if -the writing processy is stopped to completely erase -a given scan, the .radar information normally vreceivedduring this eraseperiodfis gnot storedand is lost. Accordingly, since echo `rdata'obtained from :successive Vradar ltransmitter kpulses `is sequentially written 'upon `'the storage; target in. afprogre'ssive manneril and. isytob'eg periodically replaced with new data obtained from cyclically re substantially tubular in mounted in the center portion of the tube and consistsv 3 curring azimuth scans, cyclical erasure is required for maintaining an up to date Store of radar data.

The cyclical erasure is obtained, according to the invention, during the ybac time of the writing beam during which time the writing beam is normally turned off. In this flyback interval, the writing beam is rapidly returned to its iducial origin during the normal blanking time of the display system. The writing beam current is then turned on and the beam is deected across a portion of the storage target by means of different resolvedy deection signals to .erase apart of the previously written data just prior to,

the writing of new data.

The invention will be described in greater detail with reference to the accompanying drawing in which Figure 1 is a schematic block diagram of a scan conversion system in which progressive cyclical writing and erasing is re-V quired; Figure 2 is a series of wave diagrams helpful in understanding the system of Figure 1; Figure 3 is a pic-l torial representation of a cathode ray display in which the system of Figure 1 provides a radial erasing sweep; and

Figure 4 is a cathode ray display in which the system of Figure l provides an nii-center type of erasing sweep.

Storage vTube Structure The half-tone storage tube 1 used in conjunction with the instant invention is preferably that which is described in the previously cited Pensak application, Serial No. 259,344 filed, December l, 1951, and has an evacuated envelope 3 form. A storage target 5 is principally of a dielectric member 7, such as mica, mounted transversely to the axis of the tube envelope. An electron gun structure 9 is positioned on one side of the storage target 5 and is used to establish a charge pattern on the adjacent surface of the dielectric target member 7. This gun structure 9 is generally referred to as the writing gun and includes a cathode 11 for providing a writing beam of electrons 13, a control grid 15, a screen grid 17, a first accelerating anode 19, and a second accelerating anode 21 of the conductive wall coating type. A second electron gun 23 is mounted on the opposite side of the storage target 5 and is utilized as a reading gun. The reading gun includes a cathode 25 for producing a reading beam of electrons 26, a control grid 27, a tirst accelerating anode 29, and a second accelerating anode 30 which consists of a conductive wall coating. A persuader electrode 31 is provided for directing the returning reading beam 26, which is modulated in accordance with the stored charge, into an electron multiplier 32 for subsequently producing useful output signals.

'On the writing gun side of the dielectric member 7, a suppressor grid 33 is provided which is spaced between 0.003" and 0.010" therefrom. In intervals in which data is written on the dielectric member 7, the suppressor grid 33 is usually operated at a potential between -50 v. and -100 v. The opposite side of the dielectric member, adjacent lthe reading gun, is used to support a fme mesh metallic screen 35 which serves as a collector electrode for the reading gun beam 26. The mesh screen potential is preferably'maintained at +3 volts. Also, on the reading gun side of the target, a screen electrode 37 is mounted in a spaced relation to and for the purpose of repelling positive ions travelling toward the storage target 5.

Scan conversion system v variocoupler or a sine-cosine potentiometer of thetype shown and described at page 284, volume 17 of the M. I. T. Radiation Laboratories Series. The resolver output, comprising two components of the input wave signal proportional respectively to the sine and cosine of the orientation angle of the resolver 46, are successively applied to a mixing and clamping amplier circuit 48, a

l an antenna 54 directional in characteristic. The antenna 54 is rotated azimuthally by means 55 which includes a drive motor and a servo follow-up system. A typical servo follow-up system is shown and described at page 191, volume 22 of the M. I. T. Radiation Laboratories Series. A portion of the high power radiated energy, after reection and/ or retransmission by one or more wave reecting objects indicated at 56, is` received by a receiving antenna 58 and coupled to a radar receiver 60. In practice, a transmit-receive switching device (not shown) enables a common antenna to be used for both the transmission and reception of the radar pulse signals. The radar video signals appearing at the output of the receiver 60 are coupled through a mixer 62, the output of which is preferably applied to the control grid 15 of the halftone storage tube 1. In this manner a charge pattern corresponding to radar data in polar coordinates may be established on the storage target 5.

The method of erasing the stored chargepattern may best be understood when considering the operation of the system in the interval between any two successive Writing operations. Assuming that the pulse repetition rate of the radar system is 1000 P. P. S., the synchronizer 40 produces keying pulses spaced 1000 microseconds apart. A reason- -the differentiated pulse applied to an erasing sawtooth signal generator 66. The sawtooth output signal from the generator 66, Figure 2d, is then applied to a second or erasing sweep resolver 68. The output signals produced thereby are then successively coupled to the mixing and .clamping amplifier 48, the pentode ampliiier 50 and the deection yoke 52.

The stator of the erasing sweep resolver 68 is differently` oriented with respect to the stator of the writing sweep lresolver 44 and produces a resolvederasing sweep which may be, in a typical example, from one to several P. P. I. lines advanced `of position of writing. The displacement of the stator ofthe yerasing resolver 68 with respect to the stator of the writing resolver 46 may be controlled by a micrometer mount on the stator of the erasing resolver 68.

Coincident with the 'initiation of the erasing sweep, the output signal from the dilferentiator 64 is delayed several microseconds by a delay line 70 and the delayed signal applied Vto a pulse generator 72. The pulse generator produces an output signal which may be coupled to two different circuits, an erasing beam gate 74 and an erasing screen enabler 76. The erasing screen enabler 76, a

Figure 13'27 at page 475 of volume potential-from a writing potential of between -50 -v.and

100 v. to an erasing potential of approximately zero-volts and maintains the suppressor grid at this potential until just priorto the start of the next writing operation. Simullbylturning on'the previously blanked writing beam Tfor the .period of time required Ifor sweeping the writingbe'am `acros'sthe target to effect erasure. The type of .erasing sweep` shown in Figure 3Y ofthe drawingis thus provided. 'If 'the requirements of a particular radar system are vsuch 'that alradial erasing sweep is not satisfactory, an ""o' -ce'nter type erasing Vsweep as Shown in Figure 4 may be obtained by applying the pulse signal from the difierentiator 64 not only to the erasing sawtooth generator 66 but also to a displacement generator 77. The displacement generator may produce any desired shape of output signal such as the square wave signal illustrated in Figure 2-c. The square wave signal may be coupled to a third or offset sweep resolver 78, the output of which may be mixed in the mixing and clamping amplifier 48 with signals from the erasing sweep resolver 68 to provide a deection signal as shown in Figure 2-f. The amount of lead of the erasing sweep is determined by the relative orientation of the stators of the resolvers 46 and 68 while the amount that the erasing sweep is displaced (i. e. the extent of off-centering) is dependent upon the amplitude of signals produced by the displacement generator 77. Meanwhile, by means of suitable focus and deflection circuitry 80 and 82, the storage tube reading beam 26 may be continuously deiected across the storage target 5 with television type deection signals during both writing and erasing to provide output'signals corresponding to the stored charge pattern. These output signals obtained from the electron multiplier 32 may then be applied to a kinescope 84 to provide a visual display of the converted pattern.

By performing the above-described operations of writing during each range sweep and then erasing during each flyback interval, old data is sequentially and progressively erased in recurring radar search cycles immediately in advance of the writing of new data and an up to date store of data is maintained. Sometimes a small Wedge may appear between writing and erasure in a given sequence of operations. The size of this wedge may be controlled by adjustment of the micrometer connections coupling the erasing sweep resolver 68 to the shaft 69. Also, the wedge effect is not serious since the wedge continuously rotates with the writing strobe and no dead zone is introduced in the system. Furthermore, the extent of erasure may be adjusted such that the stored data is not completely erased. In this manner, integration of cyclically recurring signals may be obtained to effectively increase the signal-to-noise ratio of the system with which this scan conversion system is used. Also, target trails of decreasing intensity may be utilized to indicate the direction of target movement as well as the targets approximate velocity. It should be noted that the writing beam, in both writing and erasing, has a certain amount of overlap, when scanning in PPI fashion, near the center of the storage target. The overlap may cause an area of no signal at very short ranges, however, while this effect may be troublesome, the area of no signal may be reduced by controlling the erasing current and thus the beam diameter as a funciton of the position of the writing (or erasing) beam. Where the beam is near the periphery of the target (where no overlap occurs), the beam current may be substantially greater than when the beam is near the center of the target.

Thus the instant invention is adapted for use in generally any system in which scan conversion is necessary and in which the reading process does not erase the stored data. 'Ihe invention has been described with reference to the cyclical erasure of data written in polar coordinate form. This method-of-erasure is-equally applicable yto .the cyclical erasure of information-written in. B-sean|form.

kIt has been 'shown that,fwith minor variations, the system may be used with Aboth long-arid short range radars and alsolma-y be used for signal integration. .A furtheradvantageof the invention-is-that the instant invention affords anup. to date store of electrical data whereas some previous systems require completeerasure followed by a complete writing operation. Also, it should be noted lthat -the .present invention affords continuous reading during both writingand erasure.

What lis vclaimed is: t

-l. A signal storage tube system comprising, an electrical storage tube having a storage target and means for providing writing and reading electron beams, writing beam de- Election means, a first resolver coupled to said writing beam defiection means responsive to applied signals for supplying signals to said writing means defiection means during predetermined writing intervals for repetitively deecting said writing beam from a fducial point across said storage target, successive writing deflections being made progressively across the surface of said storage target in a given direction, connection means for a source of input signals for modulating said writing beam to write electrical data on said storage target during said writing intervals, a second resolver mechanically coupled to said first resolver responsive to applied signals for supplying signals to said writing beam deflection means in the intervals between successive writing intervals for deflecting said Writing beam across said storage target to erase data stored thereon in prescribed areas located in the direction of said writing, and means for continuously scanning said target with said reading beam during the intervals of writing and erasing to read the remaining data stored on said target.

2. Apparatus as claimed in claim 1 wherein said first and second resolvers have differently oriented stator members, the stator position of said second resolver leading the stator position of said first resolver.

3. A signal storage tube system comprising, an electrical storage tube having a storage target and means for providing writing and reading electron beams, writing beam deflection means, a first resolver coupled to said writing beam deection means responsive to applied signals for supplying signals to said writing beam deflection means during predetermined writing intervals for repetitively defiecting said writing beam from a ducial point across said storage target, successive writing deflections being made progressively across the surface of said storage target in a given direction, connection means for a source of input signals for modulating said writing beam to write electrical data on said storage target during said writing intervals, means effective in the intervals between said writing intervals for providing signals for controlling the potentials of electrodes within said storage tube for erasure, a second resolver mechanically coupled to said first resolver responsive to applied signals for supplying signals to said writing beam deection means in the intervals between successive writing intervals for deflecting said writing beam across said storage target to erase data stored thereon in prescribed areas located in the direction of said writing, and means for continuously scanning said target with said reading beam during the intervals of writing and erasing to read the remaining data stored on said target.

4. A signal storage tube system comprising, an electrical storage tube having a storage target and means for providing writing and reading electron beams, writing beam deflection means, a first resolver coupled to said writing beam deflection means responsive to applied signals for supplying signals to said writing beam deflection means during predetermined writing intervals for repetitively radially defiecting said writing beam from a fiducial point across said storage target, successive writing deflections being made progressively across the surface of said storage target in a given direction, connection means for a source of input signals for modulating said Writing beam to write electrical data on said storage target during said writing intervals, a second resolver mechanically coupled to said rst resolver responsive to applied signals for supplying signals to said writing beam deflection means in the intervals between successive writing intervals for deecting said writing beam across said storage target to erase data stored thereon in prescribed target areas located in the direction of said Writing, a third resolver mechanically coupled to 'said first and second resolvers responsive to applied signals for supplying signals to said writing beam deiection means for displacing said writing beam from said fiducial point for erasure, and means for continuously scanning said References Cited in the le of this patent ,UNITED STATES PATENTS 2,422,135 Sanders June 10, 1947 2,451,005 Weimerret al. Oct. 12, 1948 2,454,410 Snyder 'Nov. 23, 1948 2,547,638 Gardner Apr. 3, 1951 2,549,072 Epstein Apr. 17, 1951 2,605,461 Koehler July 29, 1952. 2,605,462 Reed et al. Iuly 29, 1952 

